docs: def registerMachine(self, machineName, adminURL):
          """
             For a server machine to participate in a site, it needs to be
             registered with the site. The server machine must have ArcGIS
             Server software installed and authorized.
             Registering machines this way is a "pull" approach to growing
             the site and is a convenient way when a large number of machines
             need to be added to a site. In contrast, a server machine can
             choose to join a site.
             Inputs:
                machineName - name of the server machine
                adminURL - URL where the Administrator API is running on the
                           server machine.
                           Example: http://<machineName>:6080/arcgis/admin
             Output:
                JSON message as dictionary
          """
          params = {
              "f" : "json",
              "machineName" : machineName,
              "adminURL" : adminURL
          }
          uURL = "%s/register" % self._url
          return self._post(url=uURL, param_dict=params,
                               securityHandler=self._securityHandler,
                               proxy_port=self._proxy_port,
                               proxy_url=self._proxy_url)